1. Field of the Invention
The present invention relates to a plasma apparatus, and a method and system for extracting an electrical signal from an electrical signal transmitting medium, for example, a temperature measuring element placed under the influence of a high-frequency wave, of a member to which the high-frequency wave is applied.
2. Description of the Related Art
For example, in an RIE-scheme plasma etching apparatus, a susceptor which supports a semiconductor wafer as an object to be processed is used as a lower electrode, and a chamber or the like opposing the semiconductor wafer is used as an upper electrode. When an RF power is supplied across the opposing electrodes, a plasma is generated by an etching gas to perform plasma etching of the wafer. When an RF power source is connected to the susceptor, the susceptor serves as a high-frequency electrode, that is, an RF cathode.
When plasma etching of this type is performed, the wafer as the object to be processed is heated by the plasma. It is confirmed that when the wafer is cooled, highly anisotropic etching can be performed. Therefore, the wafer is cooled by heat transmission by cooling the susceptor. When the temperature of the susceptor is measured, the wafer temperature can be indirectly obtained, and the influence of the wafer temperature on etching can be controlled at a constant value based on the obtained temperature. A temperature measuring element such as a platinum resistor is used to measure the temperature of the susceptor.
However, since the susceptor is used as the RF cathode, RF noise is induced and superposed on a measured temperature signal. Therefore, it is difficult to measure a temperature correctly.